The present invention relates to a resin acid composition according
to the preamble of claim 1.
A composition such as this comprises at least 60 per cent by weight
resin acids and 0 - 40 per cent by weight fatty acids. Generally, the resin and
fatty acids are saponified, i.e. they occur in the form of their salts. The rest
of the product, generally approximately 0 -3 per cent by weight of its dry matter,
consists of other constituents, which have been dissolved from the pinewood during
the pulping process (for instance unsaponified neutral compounds).
The present invention also relates to a method, according to the preamble
of claim 11, of removing extractives from cellulose pulp. In this method, the pulp
is contacted with the resin acid composition in order to dissolve the extractives
from the pulp.
In the pulping industry, wood chips are principally cooked in an alkaline
aqueous solution, wherein the fibres and the binding lignin of the wood are separated
from each other, and the lignin is dissolved in the alkaline solution. After cooking,
the pulp is washed with a countercurrent washing, whereby concentrated lignin and
alkaline cooking liquor are separated from the fibre pulp of the wood.
Besides containing lignin and pulps, wood is made up of many other
constituents. These constituents are fats and resins, which are separated in the
form of fatty acids and resin acids, by means of acidification of the spent liquor
of the pulping. The spent liquor remaining after pulping also comprises terpenes,
neutral compounds and various alcohols. There are no particular problems associated
with the production of softwood pulp. By contrast, in the production of hardwood
pulp the neutral extractives remain in the pulp, leading to adverse effects in the
production of paper and cardboard.
In their recently published article [Journal of Pulp and Paper Science
(2003), 29(1), 29-34], E. Bergelin and B. Holmbom state that in removing the extractives
in birchwood pulp, the amount of residual extractives is 0.7 - 2 kg/ton of pulp
after the washing and the bleaching stages, and that the most important constituents
of the residue are betulinol, lupeol and fatty acids. These products appear to attach
firmly to the pulp fibre. Studies by P. Fardim & al., Macromolecular Chemistry
(2002) 1-4, 2 August, 2002, demonstrate that the extractives could not be anywhere
totally removed from birchwood pulp when using acetone or acetone-acetic acid extraction.
By contrast, the removal was nearly complete when phosphate compounds were applied.
In addition, an article in the journal Eastern Pharmacist (1970), 13(148), 127-130,
states that betulinol-acetate, too, is found in birch. It is evident that during
pulping this compound is changed into betulinol.
Betulinol and lupeol are both compounds known as triterpenes, which
have four combined six-ring structures and one attached five-ring structure. In
betulinol, there is a -CH2OH group, whereas in lupeol, there is a -CH3
Being hydrophobic compounds, betulinol and lupeol accumulate on their
surfaces sticky compounds, and these compounds have an adverse effect on the paper
production, because, by accumulating together, they form greasy spots on the paper,
and by forming spots that repel printing ink on the printing bed they affect the
quality of the printing on the paper. In addition, larger amounts of extractives
cause web breaks on the paper machine. Furthermore, according to some studies, the
extractives decrease the brightness of paper (US Patent Specification No. 4,444,621).
Many methods and products have been developed for removing the extractives
at different stages of pulp production.
US Patent Specification No. 4,673,460 describes how wood chips are
treated both before and during pulping with ethoxylated acrylic phenol compounds
and with a sulphonated fatty acid. Generally, the treatment is carried out by applying
compounds that have dispersive effects, such as in the solution according to US
Patent No. 6,525,169, where the reactive products derived from the interaction of
oligo-hydroxy-alkane and epichlorohydrin, as well as certain amines, are used to
remove harmful agents by means of emulsification during the paper production process.
According to US Patent No. 5,501,769, resin is removed by introducing
esters of polyoxyalkyleneglycol of fatty acids into the pulping.
In US Patent No. 4,444,621, resin compounds are removed and the brightness
is improved at alkaline conditions and in the presence of peroxides, and subject
to a quite powerful mechanical treatment.
US Patent No. 5,702,644 discloses a solution in which extractives
are removed by dispersing them using a cationic guar-compound, which comprises a
hydroxy-propyl triammonium group.
In Finland, the traditional way of attempting to remove the extractives
during pulping, in particularly from birchwood pulp, has been to add tall oil or
resin soap products into the pulp. A typical resin soap is a product that comprises
totally not less than approximately 70 % resin acids and approximately 20-25 % fatty
acids, which means that according to typical analyses, the abietic acids (approximately
28-29 %) and the dehydroabietic acid (22-23 %) are the main components of the compositions,
whereas the other resin acids form 3.5 % and the unsaponified compounds 5-10 % of
the organic part of the composition. These percentages are calculated by weight.
Typically, the resin acids have been dosed as 35 % aqueous solutions
(soap solutions) to remove the extractives, which means that the amount added has
been approximately 15-25 kg soap solution/ton of pulp. Thus, it has been possible
to decrease the percentage of the extractives from the level of 1-2 % to the level
of 0.15-0.25 %, when measured as acetone extractive.
There are problems associated with the known technique. Thus, a tall
oil enriched with conventional crude tall oil and resins removes only limited amounts
of the betunol in birchwood. When the percentage of betunol before washing the pulp
is, for example, approximately 14 % of all neutral compounds, its percentage after
washing is typically approximately 48 %. In addition, typical compositions often
comprise polymerized material that is formed when tall oil is distilled in conditions
where high local temperatures are present. This polymerized material easily attaches
to the wood fibres and, in the form of hydrophobic spots, spoils the quality of
paper and reduces the pulp yield.
It is an aim of the present invention is to eliminate the disadvantages
associated with the known technique and to provide a novel solution for removing
the extractives from hardwood pulp.
Unexpectedly, we have discovered that relatively small changes in
the composition of the resin soap lead to a major change in the removal of the extractives;
to the extent, in fact, that it has been possible to reduce the use of resin soap
while at the same time still reducing the residual extractives in the pulp to less
than half, i.e. even down to the level of 0.07-0.08 %.
In the present invention, the composition of ordinary resin soap has
been changed such that the sum total of the amount of abietic acid, dehydroabietic
acid and neoabietic acid has been increased to at least 58 per cent by weight of
the dry matter of the resin acid composition, i.e. of the total amount of the resin
soap. This compares with a figure of slightly more than 50 % in existing products.
This change of approximately 10 % considerably improves the performance
of the product, to the extent that the reduction of the extractives is improved
by more than half, although the amount of resin soap used has been decreased by
More specifically, the composition according to the present invention
is mainly characterized by what is stated in the characterizing part of claim 1.
The method according to the present invention is, in turn, characterized
by what is stated in the characterizing part of claim 11.
Considerable advantages can be achieved with the present invention.
Thus, the total percentage of extractives is decreased, the washing problems are
reduced and the variations in the percentage of extractives are reduced. In addition,
in a mill test, it was unexpectedly discovered that in the process of washing the
pulp, after a treatment according to the present invention, its dry matter increases
by 2 %.
One of the beneficial properties of this new product according to
our invention is that the product contains almost no polymerized material. In other
cases polymers are typically generated when tall oil is distilled in conditions
where high local temperatures are present. They easily attach to the wood fibres
in the form of hydrophobic spots, which spoil the quality of the paper and reduce
the pulp yield.
In the following, the present invention will be examined more closely
with the help of a detailed description.
The resin acid composition according to the present invention comes
from tall oil. More specifically, at issue is a distilled tall oil rosin, TOR, which
consists mainly of resin acids, and also comprises fatty acids and neutral compounds.
According to the present invention, this product can be produced using a vacuum
distillation technique, which means that the desired composition according to a
preferable application of the present invention is generated by condensation from
the vapour phase of the distillation. We have found that a product produced in this
way is essentially free from resin or fatty acid dimers, oligomers and polymers,
and isomerized and disproportionated products which typically are a part of the
base product of the distillation. By "essentially free" we mean that the amount
of these by-products is less than 5 per cent by weight, preferably less than approximately
2 per cent by weight, of the organic part of the composition.
The composition according to the present invention can be produced
particularly by using vacuum distillation of tall oil, carried out in a distillation
column, one which has a zone of high temperature, where the surface temperature
of the heating source is not over 260 °C, and in which zone the retention time of
the feed is not over 60 minutes.
The composition of the resin acid obtained comprises at least 60 per
cent by weight of its dry matter, preferably at least 70 per cent by weight, resin
acids, which are optionally in the form of their salts, and 0-40 per cent by weight,
most suitably not over 30 per cent by weight, resin acids or their salts. Among
the resin acids typical examples are abietic acid, dehydroabietic acid, neoabietic
acid, palustrene acid, pimaric acid and sandrakopimaric acid. Typical fatty acids
are the C16...24 fatty acids, which are saturated or mainly unsaturated.
Linolic acid and oleic acid are typical examples. Besides these main constituents,
the resin acid compositions according to the present invention comprise small amounts
of other organic constituents, which have been dissolved from the pine wood during
According to a particularly preferred embodiment of the application,
the amount of abietic acid in the composition has been increased from a typical
30 per cent by weight to almost 40 % or even above that, which means that the ratio
of the abietic acid to the dehydroabietic acid is at least 1.5:1, preferably approximately
1.7...3.0:1, most suitably approximately 1.8...2.6:1, weight/weight.
The sum total of the amounts of abietic acid, dehydroabietic acid,
neoabietic acid and palustrene acid is more than 68 per cent by weight of the dry
matter of the composition. In this case, at least 58 per cent by weight of the resin
acids, preferably approximately 58-75 per cent by weight, in particular at least
60 per cent by weight, then consists of the combined amount of the abietic acid,
the dehydroabietic acid and the neoabietic acid.
In order to generate salts of resin acids and fatty acids, the resin
acid composition according to the present invention can be saponified, i.e. contacted
an aqueous solution of an inorganic alkali. These salts are soluble in water, which
means that a water soluble soap derivative can be generated from the hydrophobic
mixture of resin acid and fatty acid. From this, it is possible to produce resin
soap that is suitable for commercial purposes, one which is delivered, like existing
products, in the form of an aqueous solution with a concentration of approximately
30-50 per cent by weight. The saponification reaction of the resin acid composition
generally runs its full course which means that the unsaponified part is generally
less than 6 per cent by weight, preferably less than 4 per cent by weight, of the
total amount of the resin acids.
The product according to the present invention can be used for removing
extractives from the pulp. This pulp can be sourced from softwood, such as pine
or spruce, but, above all, the present invention is applied to pulps that are produced
from hardwood, such as birch, aspen, alder, maple, eucalyptus and mixed tropical
hardwood. The present invention can also be applied to pulps made from annual plants,
such as the dried stalks of grain, reed canary grass, reed, bagasse etc.
Generally, the pulp is produced using a chemical cooking process,
such as the sulphate, the sulphite, the organosolv or the MILOX processes, or by
using semi-chemical pulping processes. The cooking chemicals used are primarily
sodium sulphide, sodium hydroxide, soda, peroxoformic acid, peroxoacetic acid or
alcohol. More preferably the invention is applied to pulps that are produced using
the sulphate process and other alkaline methods, and processes carried out with
organic cooking chemicals.
According to a more preferable form of the application, the present
invention is used on sulphate pulp produced from birch, aspen or eucalyptus.
The pulp is contacted with a resin acid composition before the cooking,
in which case a resin acid composition amounting to 0.1-2 per cent by weight of
the dry wood amount is added into the cooking liquor of pulp, particularly hardwood
pulp, in order to separate the extractives from the pulp. According to this alternative,
the resin acids can be in acidic form in the composition which is to be added, because
the resin acids are saponified in alkaline pulping conditions and change rapidly
to become soluble in water. According to the second alternative, resin acid composition
amounting to 0.5-0.05 per cent by weight of the dry matter weight of the pulp, is
added in order to wash the pulp (particularly hardwood pulp). Because the washing
conditions are fundamentally neutral, the resin acid composition is best added in
a water soluble form, i.e. in a saponified form.
The present invention is used to reduce extractives in pulp generated
from hardwood cooking, pulp which is at least partly bleached by using oxidative
bleaching sequences. Because the extractives react with these kinds of bleaching
chemicals, the present invention can be used to intensify the bleaching and to reduce
the consumption of chemicals. As a result, the total percentage of extractives is
lowered, the changes in the percentage of extractive are reduced and the problems
associated with washing are lessened.
Evidently, the extractives of hardwood, which are the most difficult
to remove, and which remain in the pulp after cooking, are to a great extent sourced
from the bark of birch, in which case these extractives are betuline, betulinol,
lupeol and β-sitosterol, and certain fatty acids and betulaprenols. These compounds
are difficult to remove from the pulp. Especially difficult is betulinol, which,
together with its alcohol group, can form hydrogen bridges with the wood cellulose
and which crystallizes on the surface of the cellulose fibre. It is assumed that
the present invention particularly decreases the quantity of betulinol in the pulp.
One feature which is characteristic of the present invention is the
increasing of the percentage of the abietic acid, as mentioned above. As a result,
the ratio of the abietic acid to the dehydroabietic acid is considerably higher
than in tall oil products used for conventional purposes. It is not completely clear
why this may help to remove the extractives, but, without committing ourselves to
any explanatory model, a preliminary observation suggests that the rise in the quantity
of abietic acid plays a significant part in the emulsifying effect of the resin
acid product. If we presume that, besides the emulsifying effect, the physical adduction
of ring compounds to other ring compounds has a significant effect, the increasing
of the amount of abietic acid is still emphasized. The quantity of the neoabietic
acid and the dehydroabietic acid is significant, too.
It seems that the abietic acid helps to remove the crystallized betulinol
from the surface of the fibres. It is also possible that the resin acid distribution
according to the present invention helps to form micelles and thus furthers the
removal of the extractives at the washing stage.
Our results are surprising. According to the literature (E.L. Back
& al, Pitch Control, Wood Resin and Deresination, TAPPI Press, Atlanta, USA
2000, page 211, figure 4), abietic acid alone is not very suitable for removing
extractives and, according to the same source, a tall oil, where the ratio of the
fatty oils to the resin oils is 7:3 is most suitable (page 211).
However, our own research and own mill tests demonstrate quite the
This can be explained by the fact that in products with a high resin
percentage, a change of resin acids to aromatic hydrocarbons, and accompanying dimerization,
along with other polymerization have occurred. Generally these appear at the distillation
stage. These thermally generated products, at high temperatures and with long enough
retention times, do not disperse the extractives. Instead these products are adsorbed
onto the fibres. Another explanation for what we found is that there have been new
developments in the bleaching stages of the pulp production, which affects which
components are removed and at which stage. Using a mixture of fatty acid-resin a
percentage of 0.4 % was achieved instead of the former level of 1-2 %, and with
the aid of new bleaching methods, a level of 0.15-0.25 has even been obtained. According
to the present invention, a level of 0.07-0.08 % is now achieved when a resin composition
according to our invention is used. Also, 25-30 % less product, according to this
new resin composition, is needed compared with the amount of previous products used
for removing extractives.
The fatty acids in the resin acid soap products have naturally been
changed because the distillation technique has been changed. This might be important
for the substantially improved removal of the extractives, too. In any case, the
cyclic compounded resin acid has contributed to the removal of cyclic compounded
It is known from literature that in the removal of birch extractives,
a 3 % tall oil consisting of approximately 55 % fatty acids and approximately 30
% resin acids and 15 % neutral constituents has the same effect as a 0.5 % sulphonated
dodekyl benzene. Furthermore, it is known that by using a tall oil fraction, which,
according to our invention, is significantly enriched with resin acids, the dose
can be reduced to 0.6 %, where the resin acid percentage would be 0.45 %, correspondingly.
Sulphonated surface-active agents are not suitable because of their
price and because, when using them, the "tall oil" is not properly separated from
the pulping liquor after the acidification stage.
The following non-limiting example illustrates the present invention:
Two resin soap compositions, the first of which was a product according
to a conventional technique, and the second a resin soap product according to the
present invention, were fed into the cooking liquor of a birch pulping. Both were
dosed as 37 % resin soap solutions, 20 kg per ton of cellulose pulp to be produced.
Tables 1 and 2 show the composition of the products:
The acid composition of a resin soap product produced with a conventional technique
other resin acids
Resin acids in total
Fatty acids in total
The acid composition of a resin acid product according to the present invention
other resin acids
Resin acids in total
Fatty acids in total
Using the product according to the present invention, the percentage
of the extractive could be reduced to 0.08 %, when measured as acetone extractive,
while, using the commercial composition, the percentage of the extractive was 0.15
%. Independently, it has been discovered that the dry matter percentage of the pulp
processed according to the present invention was 2 percentage units higher in the
pulp washing subsequent to the cooking.